Concerns have frequently been expressed about the effects of a new policy on unit cohesion. Indeed, President Clinton's 1993 directive to the Secretary of Defense specified that a new policy on sexual orientation in the military should end discrimination in a manner "consistent with the high standards of combat effectiveness and unit cohesion our Armed Forces must maintain" (quoted in MacCoun, 1996).

Scientific research has made it clear that cohesion is not a unitary construct. Many dimensions of cohesion have been discussed in the research literature. Perhaps the most common distinction made by behavioral scientists is between social cohesion and task cohesion.

Social cohesion refers to the nature and quality of the emotional bonds of friendship, liking, caring, and closeness among group members. A group displays high social cohesion to the extent that its members like each other, prefer to spend their social time together, enjoy each other's company, and feel emotionally close to one another.

Task cohesion refers to the shared commitment among members to achieving a goal that requires the collective efforts of the group. A group with high task cohesion is composed of members who share a common goal and who are motivated to coordinate their efforts as a team to achieve that goal.

(For a comprehensive review of these concepts, as well as the research literature on group cohesion as it relates to the personnel policy, see MacCoun, 1996).

Meta-analyses of studies of the cohesion-performance relationship indicate that a modest positive relationship exists between cohesion and performance, and is greater when a group task requires high levels of coordination, communication, and performance monitoring among group members. A causal direction cannot be concluded on the basis of these correlations. The authors of one study even asserted that the effect of success on cohesion appears to be greater than the effect of cohesion on performance (Mullen & Copper, 1994), although the authors of another study (Gully et al., 1995) argued that too few appropriate studies are currently available to permit any conclusion about causality.

Task cohesion may be more important than social cohesion in enhancing group performance. After reviewing military and civilian studies of cohesion and performance, Professor Robert MacCoun (1996) concluded that it is task cohesion — not social cohesion or group pride — that drives group performance. He pointed out that when social cohesion is too high, deleterious consequences can result, including excessive socializing, groupthink (the failure of a highly cohesive group to engage in effective decisionmaking processes), insubordination, and mutiny.

MacCoun also concluded that the impact — if any — of a new Pentagon policy concerning sexual orientation would be on social cohesion. Because coworkers can perform effectively as a team without necessarily liking each other, he argued, such a reduction in cohesion would be unlikely to reduce the military's ability to complete its mission successfully. Nevertheless, introduction of a homosexual man or woman into a work group could conceivably affect performance if he or she were ostracized from the group. MacCoun suggested that whether complete ostracism occurs would probably depend primarily on whether the unit's other members would refuse to cooperate with each other to accomplish the group's mission, and in part on the gay person's performance and demeanor. He concluded:

Although concerns about the potential effect of permitting homosexuals to serve in the military are not groundless, the likely problems are not insurmountable, and there is ample reason to believe that heterosexual and homosexual military personnel can work together effectively. The presence of acknowledged homosexuals may reduce social cohesion in some units, but seems unlikely to undermine task cohesion. Research indicates that it is not necessary to like someone to work with them, so long as members share a commitment to the group's objectives. If there is a reduction in social cohesion, it will probably involve some degree of ostracism of the homosexual, rather than a complete breakdown of the unit. Whereas some heterosexuals might refuse to cooperate with known homosexuals, many factors will discourage this and promote teamwork: effective leadership; military norms, roles, regulations, and disciplinary options; and external threats and challenges. (MacCoun, 1996, p. 172)